Soil pH and aridity influence distributions of branched tetraether lipids in grassland soils along an aridity transect

Branched glycerol dialkyl tetraethers (brGDGTs) are membrane lipids of certain soil bacteria, and their relative distributions used as a proxy for air temperature pH. While is recorded by the degree methylation, pH reflected amount internal cyclization abundance 6-methyl isomers. Since exact producers brGDGTs remain enigmatic, mechanisms underlying empirical relationships with pH, thus reliability brGDGT-based paleorecords, not well understood, especially in arid regions where mean annual precipitation (MAP) less than 500 mm. Here, we evaluate influence aridity on brGDGT grassland soils along an transect (MAP = 173–415 mm) Inner Mongolia. absolute fractional increases increasing aridity, following trend global surface calibration dataset, does not. This indicates that regions, reconstructions based contribution likely more reliable those cyclization. Furthermore, 5- respond differently to supporting prior suggestions distribution could be result changes bacterial community composition instead direct physiological alteration molecular structures source organisms. Analysis same Acidobacteria, phylum hosting potential source-organisms, shows poor relationship aridity. Instead, Verrucomicrobia (r2 0.70, p < 0.01), its subclass Spartobacteria 0.01) particular, show significant negative correlation resembling 5-methyl brGDGTs. Similarly, Actinobacteria positively correlated 0.59, The ability cultures produce iso-C15:0 fatty acids serve building blocks hints possibly soils.